Method of treating bodies of semiconductive material by chemically etching with an acid etching liquid



United States Patent s 194 703 METHOD OF TREATlNG BODIES or SEMICON-DUCTIVE MATERIAL BY CHEMICALLY nrcrr- ING WITH AN ACID ETCHING LroUnoWee been proposed to dilute etching liquids, which have been obtained bymixing concentrated nitric acid and concentrated hydrofluoric acid, withglacial acetic acid instead of with water. It appeared that thepossibility of etching Jan Bloem, Nijmegen, Netherlands, assignor toNorth 5 pits occurring had decreased somewhat but in the case AmericanPhilips Company, Inc., New York, N.Y., a of strong dilutions withglacial acetic acid, the etching corporation of Delaware rate of thisetching liquid decreases discontinuously to No Draw ing Filed June 29,1962, Ser. No. 206, extremely low values when increasing the dilution.Clams l s apphcatkoglgetheflandsJuly 1961 The object of the invention isto provide an etching 3 Claims? 156 17) liquid which does not have theabove drawbacks.

According to the invention, the etching liquid contains The inven ionrelates to a met d O treating Semisulphuric acid. It has appeared thatthe presence of the conductor bodies by chemically etching with an acidsulfuric acid counteracts the occurrence of etching pits etching liquidwhich contains hydrofluoric acid and at d the roughening f th f ce,least one oxidizing agent. Such semiconductor bodies The way in whichthe presence of sulfuric acid inhibits are used, for example, insemiconductor electrode syssurface roughening is not fully understood,but it may @1118, Such flstfansistors Crystal diodes and photoelectricbe that sulphuric acid interferes with the corrosive action cells. t ofthe liquid due to the presence of water in it by binding Whenmanufacturing such electrode systems, the Sem water chemically and thusinactivating it for corrosive conductor bodies used are generallysubjected to etching ti I treatments, for example to give the body therequired Sulphuric acid may be added, for example, in the formthickness, remove Certain Portions, t0 Clean th of concentratedsulphuric acid to any desired percentage. surface of the body or topolish a rough surface. Such Preferably the etching liquid contains atleast 30% by etching treatments may be applied to such semiconductorweight of sulphuric acid. In practice, preferably a sulbody both beforeand after providing the electrodes. The phuric acid content of at least60% and at most 85% above etching liquids may contain as oxidizingagent, for is used for improving reproducibility of the thicknessexample, nitric acid and/or hydrogen peroxide, if dereduction withoutreducing the etching rate to a less sired combined with a little bromineor iodine. practical low value.

Processes of chemically etching semiconductor bodies Just as for theknown etching liquids, it holds that the should not be confused withprocesses of electro-chemirate at which the liquid etches is alsodependent on the cally etching semi-conductor bodies, the latterprocesses ratio between the quantities of the oxidizing agent andrequiring the use of electrodes in an etching liquid, one of thehydrofluoric acid in this li uid, If the tching of which may beconstituted by the semiconductor body liquid consists of hydrogenperoxide, hydrofluoric acid, to be treated, an electrical potentialdifference between sulfuric acid and water, the content of hydrogenperoxide the electrodes being applied from the exterior, whereaspreferably is at least 50% by weight and at most 150% chemical etchingrequires the immersion of a semiconducby weight with reference to thequantity by Weight of tor body in an etching liquid only. Liquids ofquite hydrofluoric acid used in the etching liquid. The contentdifferent constitution are chosen for the two processes, the ofhydrofluoric acid with reference to the quantity of liquids for theelectroyltic etching processes normally water used in the etching liquidpreferably is at least being not able to attack the semiconductor bodywithout 10% by weight. the application of electrodes and a potentialdifference In order that the invention may readily be carried betweensaid electrodes. into effect, it will be now described more fully, byway of When using high concentrations of oxidizing agents and example,with reference to the table below, enumerating hydrofluoric acid in theetching liquids, etching occurs examples of etching liquids and theiraction upon platerapidly and is consequently less reproducible.Thereshaped germanium bodies at atemperature of 25 C. The vfore, oftendilute aqueous solutions were used to cause germanium bodies had beenobtained by sawing from a the etching treatment to occur more slowly andin a mono-crystalline germanium rod in directions at right betterreproducible manner. However, it has appeared angles to a l11 -axisfollowed by mechanical grinding that the surface of the treated bodyoften showed irreguto a thickness of 250 2, in which a somewhat roughsurlarities, for example etching pits, and could even be comface isformed. All the etching liquids have been obparatively rough. Suchirregularities in the surface may tained by mixing a 48% aqueoussolution .of hydrofluoric have a disturbing effect on the furthertreatment of the acid, a 30% aqueous solution a hydrogen peroxide andsemiconductor body for manufacturing semiconductor concentratedsulphuric acid (96%). The decrease in electrode systems, for examplewhen diffusing action imthickness per minute stated in the table relatesto a purities, and may in addition be less favourable for the decreasein thickness by the action of the etching liquid properties of such anelectrode system. It has already on oppositely located surfaces ofgermanium bodies.

Table Parts Parts by Parts by Decrease by vol by vol. vol. of PercentPercent Percent Percent inthick- Etching liquid of HF- of H20; eoncenbyWeight by weight by weight by weight ness in solution solution trated ofH10 01H of H202 of H1804 /min.

It is noted that it has appeared that the decrease in thickness perminute as stated in the table is not dependent onthe conductivity typeof the specific conductivity of the body. It has also appeared that thedecrease in thickness per minute is larger at higher'temperatures,namely increases approximately by 6% per C.

Smooth surfaces Were obtained using the freshly prepared etching liquidsstated in the above table. comparatively rapid etching liquids A and Bgive a noticeable rounding of the sharp edges of the threated bodies.The etching liquids C and G give better'reproducible results and norounding of sharp edges.

For good comparison in the above table, etching liquids were mentionedby way of example Which contained hydrogen peroxide as the oxidizingagent, while the etching effect is indicated with respect to germaniumbodies. However, the invention is not restricted to the use of hydrogenperoxide or to the etching of germanium bodies,

For example, for silicon bodies also etching liquids may 'be used whichcontain one or more oxidizing agents, hydrofluoric acid and sulphuricacid.

What is claimed is:

1. In the manufacture of a semiconductor device, a method of chemicallyetching a serniconductive body selected from the group consisting ofgermanium and siliagree The' con, comprising the step of subjecting asurface portion of the said body to the etching action of an acidetching aqueous solution containing hydrofluoric acid, at least oneoxidizing agent selected from the group consisting of hydrogen peroxideand nitricacid, and further containing between about by Weight andbyweightof sulphuric acid. 7 a 1 y 2. The method set in claim 1 whereinthe hydrofluoric acid content of the aqueous solution is at least 10% byWeight of the Water content of the aqueous solution.

3. The method set forth in clairn'Z wherein the oxidizing agent contentof the aqueous solution is at least 50% by weight of the quantity byWeight of the hydrofluoric acid content of the solution. 7 i

References Cited hytheExaminer UNITED STATES PATENTS t 1,777,321 10/30Meth 252v79.3 XR 2,337,062" 12/43 Page l56i18 XR 2,542,727 2/51 Theurer156-17 2,847,287 8/58 Landgren' '156 18 XR 2,860,039 11/58 Margulies156-18 EARL M. BERGERT, Primary E rrrirr r. JOSEPH STEINBERG, Examiner.

1. IN THE MANUFACTURE OF A SEMICONDUCTOR DEVICE, A METHOD OF CHEMICALLYETCHING A SEMICONDUCTIVE BODY SELECTED FROM THE GROUP CONSISTING OFGERMANIUM AND SILICON, COMPRISING THE STEP OF SUBJECTING A SURFACEPORTION OF THE SAID BODY TO THE ETCHING ACTION OF AN ACID ETCHINGAQUEOUS SOLUTION CONTAINING HYDROFLUORIC ACID, AT LEAST ONE OXIDIZINGAGENT SELECTED FROM THE GROUP CONSISTING OF HYDROGEN PEROXIDE AND NITRICACID, AND FURTHER CONTAINING BETWEEN ABOUT 60% BY WEIGHT AND 85% B YWEIGHT OF SULPHURIC ACID.